In community area or cable television (CATV) systems over long stretches of coaxial distribution runs, the broadband television signals are amplified at spaced locations by distribution amplifiers. The broadband television signals are transmitted over the distribution network from a headend in a forward direction to a plurality of subscribers, which is generally termed one-way system. However, more complex systems include a reverse signal path which is routed around the distribution amplifiers. The reverse channel is used for system control, messaging, pay per view events, monitoring, etc. To allow the forward signal path and the reverse signal path to use the same coaxial cable without interference, one diplex filter is used on the input of the forward signal amplifier and output of the reverse signal amplifier and another diplex filter is used on the output of the forward signal amplifier and input to the reverse signal amplifier. A diplex filter is a three-port passive device consisting of a high pass filter and a low pass filter joined at a common port. In this configuration the diplex filters are used with the distribution amplifier and reverse signal amplifier to separate the forward traveling high frequency broadband television channels and the reverse traveling low frequency data or monitoring channels. When a CATV system does not have a reverse path, surge filters may be provided before the input and after the output of the distribution amplifiers so as to protect them from high energy transients caused by line surges which can damage the amplifier.
CATV systems presently utilize a number of combinations of surge filters and diplex filters in their typical configurations. Some distribution amplifiers accommodate plug-in surge filters or diplex filters while other amplifiers have diplex filters built onto their printed circuit board. In the case of plug-in surge filters, generally only forward amplifiers for one-way systems are equipped with such filters. When these amplifiers are upgraded to a two-way system, the amplifier configuration is provided with a set of plug-in diplex filters to replace the surge filters. In other configurations, diplex filters are either built on or plugged into the amplifier printed circuit board and the amplifier is configured at the manufacturing point as a one-way (forward only) product.
There are several disadvantages to surge and diplex filters as they are presently provided for distribution amplifiers in CATV systems. Initially, surge filters are more costly than need be because they must be manufactured as plug-in assemblies to preserve the option of activating the reverse path of a particular system. Considerable cost is associated with interface hardware, a cover, and an additional printed circuit board. Present day plug-in surge filters are rendered useless when the system is upgraded to have a reverse path and are therefore wasted. Conversely, in products which do not offer plug-in surge filters, diplex filters are built on or plugged into the amplifier printed circuit board even when the amplifier is configured only as a forward only product. This results in an unnecessary cost burden when there are no plans to upgrade to a two-way system.